In recent years, since it becomes evident that a gate oxide film is oxy-nitrided in gas atmosphere such as NO or N2O, and nitrogen atoms are piled up on an interface between the gate oxide film and a silicon substrate, thereby making it possible to improve a hot carrier reliability of an n-channel type MISFET, and restrain boron (B) penetration from a p-type polycrystal silicon gate, this oxynitridation has been practically available for use in logic products.
However, there has been a report that, if an amount of nitrogen in the interface between the gate oxide film and the silicon substrate (hereinafter, referred to as a SiO2/Si interface) is excessively increased, a p-channel type MISFET is severely degraded (for example, NBTI (negative bias temperature instability) described in 1999 VLSI Symposium Digest of Technical Paper, P. 73). Therefore, control of an amount of nitrogen in the above interface is an important task.
In addition, as a substitutive technique of an oxynitridation, for example, as described in Japanese Patent Application Laid-open No. 10-79506, it is known that a similar advantageous effect is attained by ion implantation when source and drain extensions are formed after nitrogen or a nitrogen-containing ion has been subjected to gate electrode processing. FIG. 84 shows the test result showing an example, where remarkable improvement of a hot carrier reliability is achieved by almost one hundred times in a nitrogen atom of 1×1015 cm−2 in dosage.